U.S. patent application number 09/888400 was filed with the patent office on 2002-02-07 for arc welding wire of high feeding performance and wire drawing method.
Invention is credited to Lee, Heedok, Lee, Jachyoung.
Application Number | 20020014477 09/888400 |
Document ID | / |
Family ID | 19674555 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014477 |
Kind Code |
A1 |
Lee, Heedok ; et
al. |
February 7, 2002 |
Arc welding wire of high feeding performance and wire drawing
method
Abstract
Disclosed is a wire for arc welding of high feedability having a
hardness deviation of less than 18 between a central portion and a
surface of a cross section of the wire, and a hardness deviation of
less than 15 between each interval of 200 mm in a longitudinal
direction when measured by an Hv1 hardness tester. The hardness
deviation of the wire is adjustable through control of the area, in
which the wire is in contact with dies. The present invention is
characterized by adjusting the hardness deviation of the wire by
adjusting the contact area ratio defined by the following formula.
Contact area ratio=Reduction contact ratio (Reduction contact
area/Cross section area of an incoming wire)+Correction contact
ratio (Correction contact area/Cross section area of an outgoing
wire)
Inventors: |
Lee, Heedok; (Changwon-city,
KR) ; Lee, Jachyoung; (Changwon-city, KR) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
|
Family ID: |
19674555 |
Appl. No.: |
09/888400 |
Filed: |
June 26, 2001 |
Current U.S.
Class: |
219/145.1 |
Current CPC
Class: |
B21C 1/00 20130101; B23K
35/40 20130101; B23K 35/308 20130101; B21C 1/12 20130101; B23K
35/0261 20130101; B21C 37/045 20130101 |
Class at
Publication: |
219/145.1 |
International
Class: |
B23K 035/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2000 |
KR |
10-2000-0036126 |
Claims
What is claimed is:
1. A wire for arc welding, characterized in that a hardness
deviation between a central portion of a cross section and a
surface of the wire is less than 18, and that a hardness deviation
at intervals of 200 mm in a longitudinal direction of the wire is
less than 15 when measured by an Hv1 hardness tester.
2. The wire for arc welding of claim 1, wherein the hardness
deviation between the central portion of the cross section and the
surface of the wire and the hardness deviation in the longitudinal
direction of the wire are adjusted by limiting a contact area ratio
defined by the following formula to be within the range of
3-3.5:Contact area ratio=Reduction contact ratio (Reduction contact
area/Cross section area of an incoming wire)+Correction contact
ratio (Correction contact area/Cross section area of an outgoing
wire)
3. A method of drawing a wire for arc welding claimed in claim 1 to
draw the wire to have a desired diameter, the method comprising two
final drawing steps of: reducing a hardness deviation between a
central portion of a cross section and a surface of the wire
through adjustment of a contact angle of the wire with dies; and
reducing a hardness deviation in a longitudinal direction of the
wire through adjustment of a length of a bearing part, in which the
wire is corrected.
4. A method of drawing a wire for arc welding claimed in claim 2 to
draw the wire to have a desired diameter, the method comprising two
final drawing steps of: reducing a hardness deviation between a
central portion of a cross section and a surface of the wire
through adjustment of a contact angle of the wire with dies; and
reducing a hardness deviation in a longitudinal direction of the
wire through adjustment of a length of a bearing part, in which the
wire is corrected.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a wire for arc welding, and
in particular, to a wire for arc welding, which has enhanced
feedability by uniformly distributing residual stress of the final
wire product.
[0003] Wire is added as a filler metal for the mechanism of arc
welding. To be specific, wire is wound around a spool or a pail
pack for welding, and passes through a feeding roller and a welding
torch cable. The wire is then melted by an electric arc heating so
as to be welded with a base metal. Therefore, it is critical to
secure a high feedability for stable welding. Further, in the light
of the recent welding work seeking automation and high efficiency,
it is mandatory to provide a stable feeding of wire in a rapid
feeding velocity. Thus, the demand for enhancing feedability of
wire is increasing.
[0004] 2. Description of the Related Art
[0005] In a variety of wires including the one for arc welding, an
initial rod passes through dies of diverse sizes, and is drawn to
be a final wire product after undergoing steps of reducing diameter
thereof to be thinner.
[0006] In the wire drawing process, the factors related to wire
feedability may be a wire drawing schedule in accordance with the
reducing ratio for drawing the wire to have a desired diameter,
distribution of internal stress through adjustment of deviation of
a tensile strength or an drawing ratio of wire, straightness of
wire, etc. Of those, an uniform distribution of internal stress of
the wire is a critical factor to be considered in enhancing the
wire feedability.
[0007] The conventional method of controlling a wire drawing
process to enhance feedability of the wire was limited to
considering a reduction ratio only to reduce the thick diameter of
the wire to be thinner or an uniform distribution of the internal
stress through adjustment of deviation of a tensile strength or a
drawing ratio of the wire.
[0008] As the drawing of wire is repeated in the wire drawing
process, however, the external portion of the wire, i.e., the
surface of the wire, with which the dies are in contact, becomes
denser than central portion of the wire and is hardened. As the
surface of the wire is hardened, it is impossible to draw a wire,
and the distribution of residual stress between the external
portion and the central portion of the wire becomes irregular.
Therefore, the conventional control focused on a mere adjustment of
the wire drawing schedule in accordance with the reducing ratio or
an adjustment of the tensile strength has a limit in achieving a
uniform distribution of residual stress between outside and inside
of the final wire product.
[0009] Further, the hardness of surface of the wire resulting from
the repeated drawing thereof causes an abrasion of the dies, which
are in contact with the wire, and causes irregular surface and
damaged surface of the drawn wire, thereby lowering the quality of
a final wire product and preventing a smooth wire feeding in the
course of welding.
[0010] The abrasion of dies caused by contact with wire having a
hardened surface results in an irregular contact area, which is in
contact with the wire, and further results in an irregular
distribution of the residual stress in the longitudinal direction
of the final wire product. Accordingly, when the wire passes
through a feeding roller and a welding torch cable in the course of
welding, the load is partially concentrated, thereby causing
failure of wire feeding because of entanglement and twist of the
wire.
SUMMARY OF THE INVENTION
[0011] It is, therefore, an object of the present invention to
enhance a feedability of a wire for arc welding by uniformly
distributing an internal stress of the wire through adjustment of
the hardness deviation of a cross section and in a longitudinal
direction of the wire in the wire drawing process.
[0012] Another object of the present invention is to provide a wire
for arc welding having a uniform distribution of residual stress of
the wire by controlling an area, in which the wire is in contact
with dies, and by reducing hardness deviation of the wire.
[0013] Still another object of the invention is to provide a method
of drawing a wire for arc welding that divides the final wire
drawing step in an ordinary wire drawing process into two steps,
whereby a hardness deviation between a central portion of the cross
section and a surface of the wire is reduced through adjustment of
the contact angle between the wire and the dies in the first step,
and the hardness deviation in the longitudinal direction of the
wire is reduced through adjustment of the length of a bearing part
in which the wire is corrected.
[0014] To achieve the above objects, there is provided a wire for
arc welding having a hardness deviation of less than 18 between a
central portion and a surface of a cross section of the wire, and a
hardness deviation of less than 15 between each interval of 200 mm
in a longitudinal direction when measured by an Hv1 hardness
tester.
[0015] The hardness deviation of the wire is adjustable through
control of the area, in which the wire is in contact with dies. The
present invention is characterized by adjusting the hardness
deviation of the wire by adjusting the contact area ratio defined
by the following formula.
Contact area ratio=Reduction contact ratio (Reduction contact
area/Cross section area of an incoming wire)+Correction contact
ratio (Correction contact area/Cross section area of an outgoing
wire)
[0016] As a technical concept to achieve the above objects, there
is also provided a method of drawing a wire for arc welding to have
a desired diameter, the method of finally drawing a wire comprising
the steps of: reducing a hardness deviation between a central
portion and a surface of a cross section of the wire through
adjustment of a contact angle between the wire and dies; and
reducing a hardness deviation in the longitudinal direction of the
wire through adjustment of the length of a bearing part in which
the wire is corrected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description when taken in conjunction with the
accompanying drawings, in which:
[0018] FIG. 1A is a transversal section view of a wire passing
through a feeding roller;
[0019] FIG. 1B is a longitudinal section view of a wire passing
through a feeding roller;
[0020] FIG. 2 is a diagram illustrating a reduction contact area
and a correction contact area when a wire passes through dies;
[0021] FIG. 3 is a diagram illustrating two divided steps of a
final wire drawing process according to the present invention;
and
[0022] FIG. 4 is a diagram illustrating a method of testing a
feedability of a wire (2-turn feedability test) according to an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] A preferred embodiment of the present invention will be
described herein below with reference to the accompanying drawings.
In the following description, well-known functions or constructions
are not described in detail since they would obscure the invention
in unnecessary detail.
[0024] FIG. 2 is a diagram illustrating a reduction contact area 20
and a correction contact area 200 when a wire W passes through dies
D.
[0025] The contact area between the wire W and the dies D is mainly
determined by the following factors: i) a contact area of the dies
D with the wire W in which actual reduction of the wire W is
performed; and ii) straightness of the wire and a contact area of
the wire W with a bearing part 200 in accordance with the
straightness. The diameter of the wire is corrected by a bearing
part 200 so as to have an enhanced straightness.
[0026] In case of the factor i), when the contact area of the
portion where the wire W is actually reduced (i.e., the reduction
contact portion) is excessively small, the difference of residual
stress between inside of the (circular) section (i.e., central
portion) and outside (surface) of the wire W becomes greater. This
results in a greater difference of hardness between one outside and
the other outside of the wire W. As a consequence, the wire W is
twisted if it fails to resist continuous partial load (refer to
FIGS. 1A and 1B) laid thereon when the wire W passes through a
feeding roller in the course of welding, thereby resulting in
vibration of the tip of the wire W that might cause an arc
instability. Further, when the contact area of the portion where
the wire W is actually reduced is excessively large, a partial work
hardening occurs, thereby lowering the quality of surface of the
wire W. In the worst case, the partial stress deviation between the
inside (central portion) and outside of the wire W becomes greater,
thereby disabling drawing of the wire W.
[0027] In case of the factor ii), when the contact area of the wire
W with the bearing part 200 is excessively small, the deviation of
the internal stress in the longitudinal direction of the wire W
becomes greater, and the feeding of the wire W is not smoothly
performed. As a consequence, the wire W fails to bear continuous
partial load laid thereon when the wire W passes through a feeding
roller 1, and is entangled or twisted, thereby causing a departure
of the wire W from the feeding roller 1 or a bending of the wire W.
Thus, the wire W is likely to be deformed after passing through the
feeding roller 1 or a cable in the welding process. The deformed
wire has no straightness after passing through a contact tip,
thereby causing a defect in welding (i.e., a bead meandering).
[0028] The conventional method of controlling such a deviation of
internal stress employed a manner of controlling a tensile strength
or a drawing ratio of a wire product by means of a stable reduction
ratio. However, this manner has a limit to controlling a stress of
the external surface of the wire W receiving a load in the feeding
as well as of the central portion of the wire W receiving the load
from the external surface.
[0029] Under these circumstances, the inventors of the present
invention have discovered and conceived the fact that the internal
stress of the wire can be uniformly distributed by controlling the
total area. The total area can be obtained by summing a reduction
contact area, which is an area of the reduction contact portion 20
that is actually reduced when the wire W passes through dies, and a
correction contact area, which is a correction contact portion 200
where diameter of the wire W is corrected.
[0030] The inventors of the present invention have discovered
another fact that distribution of the residual stress of such a
final wire product is closely related to a hardness deviation
between the central portion of a cross section and the surface of
the wire as well as to a hardness deviation in the longitudinal
direction of the wire. To be specific, the inventors have
discovered that the physical property of the wire itself relating
to enhancement of the feedability of the wire is affected by an
uniform distribution of the internal stress in accordance with the
reduction of the hardness deviation of the cross section of the
wire and in the longitudinal direction of the wire, and that the
reduction of the hardness deviation can be achieved by controlling
the contact area of the wire with the dies to be within a
preferable range. With respect to control of the contact area, it
is important to control the final drawing steps in the wire drawing
process.
[0031] The wire drawing process is usually performed in multiple
drawing steps to produce a wire having a thin diameter. However,
all the internal stress residing in the wire in the multiple
drawing steps is reflected in the wire immediately before taking
the final drawing step. Accordingly, it is critical to control the
residual internal stress of the wire in the final drawing step.
[0032] To be specific, the final drawing step is divided into two
steps as shown in FIG. 3. In the first step, the contact angle of
the wire W with the dies D is lessened to reduce the hardness
deviation of a cross section of the wire W and subsequently to
prevent vibration of the tip of the wire W caused by distortion of
the wire. In the second step, the length of the bearing part of the
dies, i.e., the length of the bearing part 200, in which the wire
is corrected, is elongated to reduce the hardness deviation in the
longitudinal direction of the wire W and subsequently to prevent
defect of welding (bead meandering) caused by bending or twisting
of the wire when passing through a cable.
[0033] The present invention is characterized in that the residual
stress of the wire is drastically decreased by controlling the
contact area ratio to be within the range of 3-3.5, whereby the
hardness deviation between the central portion of the cross section
and the surface of the wire and the hardness deviation in the
longitudinal direction of the wire are reduced. A contact area
ratio is defined by summing a value of a reduction contact area
ratio and a value of a correction contact ratio with respect to two
dies.
[0034] The following is a detailed description of a preferred
embodiment of the present invention.
[0035] Embodiment
[0036] To study a relation between the hardness deviation between
the central portion of the cross section and the surface of the
wire and the hardness deviation in the longitudinal direction of
the wire and a weldability, weldability was evaluated based on a
wire for stainless, which is relatively more stressful to work
hardening in the drawing process.
1 TABLE 1 Hardness deviation (Hvl) Cross Feeding Classifi- Contact
Section of Longitudinal Load cation Area Ratio the Wire Direction
(A) Remarks Present Invention 1 3.4 10.5 10.4 1.8 2 3.3 11.0 5.0
1.5 3 3.1 9.5 16.1 2.2 4 3.5 12.8 7.3 1.7 5 3.0 18.5 10.5 2.1
Comparative Example 6 2.1 20.0 16.4 2.6 7 2.5 18.5 15.5 2.4 8 2.3
19.5 16.0 2.5 9 2.4 18.4 15.8 2.5 10 14.1 3.6 Heat Treated Wire
[0037] Reduction of the wire is performed to be 5.5 mm.fwdarw.1.2
mm, and a kind of the applicable steel is AWS ER309, JIS Y309. The
feedability was tested in 2-turn form as shown in FIG. 4, and the
welding condition was 190A-220V. The wire drawing process was
performed in the order of: 1.sup.st drawing.fwdarw.heat
treatment.fwdarw.2.sup.nd drawing3.sup.rd drawing (final drawing).
The final step of wire drawing step was divided into two steps, and
the hardness measured by means of a Vickers hardness tester
(hereinafter, referred to as an "Hv1 ") with respect to each wire
after changing the contact area ratio in each of the wire drawing
steps (of the final wire drawing process).
[0038] The heat treatment is performed after the first drawing and
before the final drawing. The heat treatment performed after the
first drawing is the one to release the work hardening of the drawn
wire for the next drawing because stainless steel is stressful to
work hardening. The heat treatment performed before the final
drawing is to minimize and uniformly distribute the internal
residual stress of the final wire product because a distribution of
the residual stress of the incoming wire is as much significant as
releasing the stress of the wire when passing through dies. The
heat treatment performed before the final wire drawing is also
important because even if the stress is released more or less after
the 1.sup.st drawing, the residual stress distribution can scarcely
be achieved to a desirable extent due to the continued 2.sup.nd
drawing that causes irregular distribution of the internal residual
stress.
[0039] The hardness deviation of a cross section of the wire was
obtained by measuring the hardness of the central portion of the
section and the surface of the wire, while the hardness deviation
in the longitudinal direction of the wire was obtained by
consecutively measuring the hardness five times at intervals of 200
mm and by arithmetically averaging the measured values
(arithmetical average value of three test samples).
[0040] As described above, the final drawing (i.e., the 3.sup.rd
drawing) step was divided into two steps. In the first step, the
reduction contact area was controlled through adjustment of the
contact angle of the wire with the dies. In the second step, the
correction contact ratio, i.e., the correction contact area in the
step of correcting the diameter of the drawn wire, is controlled,
and the hardness deviation between the central portion of the cross
section and the surface of the wire and the hardness deviation in
the longitudinal direction of the wire are reduced to uniformly
distribute the residual stress of the wire. In other words, the
hardness deviation of the cross section of the wire is reduced by
lessening the contact angle of the wire with the dies to prevent
vibration of the tip of the wire caused by twisting of the wire in
the first step of the welding process. In the second step, the
hardness deviation is reduced in the longitudinal direction of the
wire by elongating the length of the bearing part, in which the
wire is corrected, to prevent defect of welding (bead meandering)
caused by bending or twisting of the wire when passing through a
cable. The degree of contact angle of the wire with the dies in the
first drawing step and the degree of contribution of the bearing
part to the contact area ratio in the second drawing step are
preferably 1/3(1-1.17)-1/2(1.5-1.75), approximately, provided that
the contact area ratio is 3-3.5.
[0041] As shown in the Table 1 above, the feeding load is most
stable when the hardness deviation between the central portion and
the surface of the wire, i.e., the hardness deviation of the cross
section of the wire is less than 18, and the hardness deviation in
the longitudinal direction is less than 15. In case of the Examples
1, 2 and 4 showing the hardness deviation between the central
portion of the cross section and the surface of the wire and the
hardness deviation in the longitudinal direction of the wire to be
within the preferable range, the feedability becomes higher and the
arc becomes stable as the feeding load becomes lower. In case of
the Examples 3 and 5, however, any one of the hardness deviation
values of the cross section or the longitudinal direction is out of
the preferable range, and the feeding load tends to be higher. This
phenomenon is because the contact area ratio is composed of
summation of the reduction contact ratio and the correction contact
ratio. The phenomenon also signifies that a stable feedability can
be secured not only when the total of the contact area ratio is
controlled within a preferable range but also when the reduction
contact ratio and the correction contact ratio as well are
controlled within a preferable range.
[0042] In a 2-turn welding test of a wire, arc becomes unstable
when the feeding load is about 2.1. When the feeding load is higher
than 2.1, however, welding can be performed but welding cannot be
consecutively performed due to instability of arc.
[0043] As described above, the feedability can be enhanced by
controlling the hardness deviation between the central portion and
the surface of the wire to be less than 18 and the hardness
deviation at intervals of 200 mm in the longitudinal direction of
the wire to be less than 15, when measured by an Hv1 hardness
tester so as to uniformly distribute the residual stress of the
wire.
[0044] The present invention provides a wire for arc welding with
uniform distribution of residual stress of the wire by controlling
the contact area of the wire with dies to be within a preferable
range so as to reduce hardness deviation of the wire. As a specific
method, the present invention provides a wire drawing method by
dividing the final drawing step into two steps.
[0045] While the invention has been shown and described with
reference to a certain preferred embodiment thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *